PURPOSE: To enhance the workability and to automate the working of a cylindrical workpiece by attaching a cover to only a lower opening in the cylindrical workpiece, and by attaching the workpiece with the use of a fastening device mounted on a turret through one-touch manipulation.

CONSTITUTION: A fixed hydraulic cylinder 20 gives vertical motion to the center shaft 18 of a cylindrical workpiece 14a rotatably held between upper and lower turrets, and accordingly, the cylindrical workpiece 14a is fastened and released by this vertical motion. An upward facing cover 28 is fixed to the lower end of the center shaft 18 of the cylindrical workpiece 14a so that a lower opening in the cylindrical workpiece is covered with and fastened by the cover 28 during descent of a piston rod 22. In order to stop the turrets at a predetermined position, a position limit plates in the number equal to the number of rotary shafts are attached around one of the upper and lower turrets. A position limit knock is fitted in a recess formed in each of the position limit plates so as to stop the turrets at a predetermined position.